Hearing aids normally comprise at least one microphone as acoustic input element; at least one speaker as acoustic output element; and an electronic processing element, connected with said microphone and said speaker, for the processing and manipulation of electronic signals. This electronic processing element may comprise analogue or digital signal processing devices. Said elements are usually arranged within at least one main case or shell of the hearing device.
Typically, the microphone acts as an electroacoustic transducer and receives acoustic signals, converts such signals into electrical signals and transmits them to the abovementioned electronic processing element.
The electronic processing element is part of a signal processing circuit which, normally, performs various signal processing functions. Such signal processing functions can include amplification, background noise reduction, beamforming, feedback cancelling, frequency lowering, sound type classification, tone control, etc.
Normally, the signal processing circuit outputs an electrical signal to a speaker. The speaker acts as an electroacoustic transducer and converts the electrical signal from the signal processing circuit into an acoustic signal which is transmitted as audio into a user's ear. For a cochlea implant, the transducer is replaced by a set of electrodes which deliver electrical impulses directly to the hearing nerve.
For the sake of reliability, safety and efficiency in use of electronic devices, such as of hearing aids, an intelligent battery management is desirable. Especially in case of rechargeable batteries, it is desirable to manage rechargeable batteries in a way that not simply the battery lifespan is maximized, but also the usage in between successive charging cycles is adaptively rationalized, in compliance with the current situation.
Particularly for rechargeable batteries, an effective battery management is dependent on a best possible measurement of the state of charge of the power storage means employed, that is of the percentage of charge remaining.
Poor estimates of such state of charge may lead to over-charging or over dis-charging, ultimately resulting in reduced battery lifetime and usage performance. Charging not in line with the current state of charge or based on erroneous estimates thereof may eventually cause breakdown, overheating and uncontrolled venting of the power storage means, up to explosion.
It is known, in the prior art, relating the charge remaining accumulated in power storage means to voltage measurements at the terminal of such power storage means. Thus, measurements of the terminal voltage are used to calculate the remaining charge level, or capacity, of power storage means.
On the other hand, even though the correlation between voltage and state of charge of the power storage means is strong—for instance, for Li-Ion batteries—, voltage correlation techniques still suffer from conversion inaccuracies. In particular, the electronic circuitry of the electronic devices in question can itself introduce circuit offset errors to the measure of the voltage of power storage means.
Such voltage offset errors, inherent to the electronic circuitry, can have a significant impact on the measurement of voltage and need to be taken into account, and compensated for, when trying to determine the actual remaining charge level, or capacity, of power storage means. If the offset voltage error is not tuned, or is wrongly tuned, an estimate of the state of charge of a battery can be easily off by 20%.
U.S. Pat. No. 7,999,515 B2 discloses a system for operating a rechargeable battery which takes into account an offset error when charging said battery to a predetermined maximum voltage.
The calibration process as described in U.S. Pat. No. 7,999,515 B2 adopts a traditional approach, by performing the calculation of the offset error to be compensated for while the battery is connected to an external power supply, charging the battery via a charge controller. The calculation of the offset error according to U.S. Pat. No. 7,999,515 B2 is carried out under conditions wherein there is virtually no load on the rechargeable battery. A known, explicitly predetermined maximum voltage is therefore applied to the rechargeable battery while an external power supply is made available.
The calibration process described in U.S. Pat. No. 7,999,515 B2 is suitable for conventional operations aimed at measuring and characterizing a tuning parameter for compensation of a voltage-offset error already at a testing phase or anyway at a stage substantially integral with the production steps. Testing and/or production typically happen at the hand of an electric device manufacturer.
Such a tuning adds to the overall complication and lengthiness of production procedures encountered by an electric device manufacturer. Moreover, such a tuning is disconnected from the actual conditions under which the electric devices—provided with the rechargeable batteries whose state of charge is to be gauged—are going to be employed by the end users.
There exists a need for a method of self-tuning the voltage of a rechargeable battery of an electronic device, and for a corresponding electronic device comprising a system for operating a rechargeable battery according to such method, which is conceived in a way that 1) the tuning can be effectively carried out without the need for the electronic device to be powered during charge via a microcontroller or similar; 2) the tuning does not have to rely on the actual, preventive knowledge of a specific predetermined voltage to be applied to the rechargeable battery and on the detection of charging currents to be delivered to the battery until predetermined charging current levels are reached; 3) the tuning does not complicate the electric device production processes; and 4) the tuning is reflective of actual operating conditions of the electronic devices.